This invention concerns a method of improving retention and drainage in papermaking processes using a diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer in combination with a cationic, structurally-modified polymer.
International Patent Application No. US01/10867, published Jan. 10, 2002, describes the preparation of structurally-modified cationic polymers and their use as retention and drainage aids in papermaking processes.
The use of medium molecular weight diallyldimethylammonium chloride/acrylamide copolymers as retention and drainage aids is reviewed in Hunter et al., xe2x80x9cTAPPI 99 Preparing for the Next Millenniumxe2x80x9d, vol. 3, pp. 1345-1352, TAPPI Press (1999).
U.S. Pat. No. 6,071,379 discloses the use of diallyl-N,N-disubstituted ammonium halide/acrylamide dispersion polymers as retention and drainage aids in papermaking processes.
U.S. Pat. No. 5,254,221 discloses a method of increasing retention and drainage in a papermaking process using a low to medium molecular weight diallyldimethylammonium chloride/acrylamide copolymer in combination with a high molecular weight dialkylaminoalkyl (meth)acrylate quaternary ammonium salt/acrylamide copolymer.
Nonetheless, there is a continuing need for new compositions and processes to further improve retention and drainage performance, particularly for use on the faster and bigger modern papermaking machines currently being put into use.
We have discovered that using a diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer in combination with a cationic, structurally-modified polymer outperforms the dual cationic coagulant/flocculant systems such as EPI:DMA/cationic polymer that are typically used for improving retention and drainage in papermaking processes. Moreover, there is an unexpected synergistic effect with the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymerxe2x80x94cationic, structurally-modified polymer combination of this invention that is not seen when a typical unmodified cationic flocculant of similar charge is used.
Accordingly, this invention is directed to a method of increasing retention and drainage in a papermaking furnish comprising adding to the furnish an effective amount of a diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer and an effective amount of a cationic structurally-modified water soluble polymer, wherein the cationic structurally-modified water-soluble polymer is prepared by initiating polymerization of an aqueous solution of from about 95 to about 5 mole percent of an acrylamide monomer of formula 
wherein R7, R8 and R9 are independently selected from H and alkyl and from about 5 to about 95 mole percent of a cationic monomer of formula 
wherein A1 is O or NH; B1 is C2-C4 alkylene or hydroxypropylene; R1 is H or CH3, R2 and R4 are independently C1-C2 alkyl; R3 is H, C1-C2 alkyl or arylalkyl; and X1 is an anionic counterion under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
Definitions of Terms
As used herein, the following abbreviations and terms shall have the following meanings.
xe2x80x9cAcAmxe2x80x9d for acrylamide.
xe2x80x9cDADMACxe2x80x9d for diallyldimethylammonium chloride.
xe2x80x9cDMAEA.MCQxe2x80x9d for dimethylaminoethyl acrylate, methyl chloride quaternary salt.
xe2x80x9cEDTA.4Na+xe2x80x9d for ethylenediaminetetraacetic acid, tetrasodium salt.
xe2x80x9cAlfonic(copyright) 1412-60xe2x80x9d for ethoxylated linear alcohol (60% ethylene oxide) available from Vista Chemical Co., Houston, Tex.
xe2x80x9cSpan 80xe2x80x9d for sorbitan monooleate available from ICI Specialty Chemicals, Wilmington, Del.
xe2x80x9cTriton(copyright) N-101xe2x80x9d for nonylphenoxy polyethoxy ethanol, available from Rohm and Haas Co., Philadelphia, Pa.
xe2x80x9cTween 61xe2x80x9d for POE (4) sorbitan monostearate, available from ICI Specialty Chemicals, Wilmington, Del.
xe2x80x9cAIBNxe2x80x9d for 2,2xe2x80x2-azobis(isobutyronitrile), available from E.I. du Pont de Nemours and Co. Inc.; Wilmington, Del.
xe2x80x9cAIVNxe2x80x9d for 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile), available from E.I. du Pont de Nemours and Co. Inc.; Wilmington, Del.
xe2x80x9cPOExe2x80x9d for polyoxyethylene.
xe2x80x9cRSVxe2x80x9d stands for reduced specific viscosity. Within a series of polymer homologs which are substantially linear and well solvated, xe2x80x9creduced specific viscosity (RSV)xe2x80x9d measurements for dilute polymer solutions are an indication of polymer chain length and average molecular weight according to Paul J. Flory, in xe2x80x9cPrinciples of Polymer Chemistryxe2x80x9d, Cornell University Press, Ithaca, N.Y., (copyright)1953, Chapter VII, xe2x80x9cDetermination of Molecular Weightsxe2x80x9d, pp. 266-316. The RSV is measured at a given polymer concentration and temperature and calculated as follows:   RSV  =            [                        (                      η            /                          η              0                                )                -        1            ]        c  
xcex7=viscosity of polymer solution
xcex7o=viscosity of solvent at the same temperature
c=concentration of polymer in solution.
The units of concentration xe2x80x9ccxe2x80x9d are (grams/100 ml or g/deciliter). Therefore, the units of RSV are dl/g. In this patent application, a 1.0 molar sodium nitrate solution is used for measuring RSV, unless specified. The polymer concentration in this solvent is 0.045 g/dl. The RSV is measured at 30xc2x0 C. The viscosities xcex7 and xcex7o are measured using a Cannon Ubbelohde semimicro dilution viscometer, size 75. The viscometer is mounted in a perfectly vertical position in a constant temperature bath adjusted to 30xc2x10.02xc2x0 C. The error inherent in the calculation of RSV is about 2 dl/g. When two polymer homologs within a series have similar RSV""s that is an indication that they have similar molecular weights.
xe2x80x9cIVxe2x80x9d stands for intrinsic viscosity, which is RSV extrapolated to the limit of infinite dilution, infinite dilution being when the concentration of polymer is equal to zero.
xe2x80x9cBased on formulaxe2x80x9d means the amount of reagent added based on the total formula weight.
xe2x80x9cBased on polymer activexe2x80x9d and xe2x80x9cbased on monomerxe2x80x9d mean the amount of a reagent added based on the level of vinylic monomer in the formula, or the level of polymer formed after polymerization, assuming 100% conversion.
xe2x80x9cPapermaking processxe2x80x9d means a method of making paper products from pulp comprising forming an aqueous cellulosic papermaking furnish, draining the furnish to form a sheet and drying the sheet. The steps of forming the papermaking furnish, draining and drying may be carried out in any conventional manner generally known to those skilled in the art. Conventional microparticles, alum, cationic starch or a combination thereof may be utilized as adjuncts with the dual polymer treatment of this invention, though it must be emphasized that no adjunct is required for effective retention and drainage activity.
xe2x80x9cStructurally modified cationic polymerxe2x80x9d means a high molecular weight water-soluble polymer prepared by initiating polymerization of a solution of (meth)acrylamide and one or more cationic monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred. The structurally modified cationic polymer may be an emulsion polymer, dispersion polymer, solution polymer or gel polymer. The structurally modified cationic polymer preferably has a RSV of from about 12 to about 40, more preferably from about 15 to about 35 and still more preferably from about 20 to about 30 dl/g and preferably comprises from about 5 to about 30, more preferably from about 7 to about 25 and still more preferably from about 9 to about 18 mole percent cationic monomer. A preferred structurally modified cationic polymer is dimethylaminoethylacrylate methyl chloride quaternary salt/acrylamide copolymer.
xe2x80x9cAcrylamide monomerxe2x80x9d means a monomer of formula 
wherein R7, R8 and R9 are independently selected from H and alkyl. Preferred acrylamide monomers are acrylamide and methacrylamide. Acrylamide is more preferred.
xe2x80x9cCationic monomerxe2x80x9d means a monomer of formula 
wherein A1 is O or NH; B1 is C2-C4 alkylene or hydroxypropylene; R1 is H or CH3, R2 and R4 are independently C1-C2 alkyl; R3 is H, C1-C2 alkyl or arylalkyl; and X1 is an anionic counterion. Representative cationic monomers include dimethylaminoethylmethacrylate benzyl chloride salt (DMAEM.BCQ), dimethylaminoethylacrylate benzyl chloride salt (DMAEA.BCQ), dimethylaminoethylacrylate methyl chloride salt (DMAEA.MCQ), diethylaminoethylacrylate methyl chloride salt (DEAEA.MCQ), dimethylaminoethylmethacrylate methyl chloride salt (DMAEM.MCQ), dimethylaminoethylmethacrylate methyl sulfate salt (DMAEM.MSQ), dimethylaminoethylacrylate methyl sulfate salt (DMAEA.MSQ), methacrylamidopropyltrimethylammonium chloride (MAPTAC), acrylamidopropyltrimethylammonium chloride (APTAC), and the like. Dimethylaminoethylacrylate methyl chloride salt and dimethylaminoethylmethacrylate benzyl chloride salt are preferred.
xe2x80x9cDiallyl-N,N-disubstituted ammonium halide/acrylamide copolymer means a copolymer of a diallyl-N,N-disubstituted ammonium halide monomer of formula
(H2Cxe2x95x90CHCH2)2N+R5R6X2xe2x88x92
wherein R5 and R6 are independently C1-C20 alkyl, aryl or arylalkyl and X is a halogen and an acrylamide monomer as defined herein. The diallyl-N,N-disubstituted ammonium halide/copolymer may be an emulsion polymer, dispersion polymer, solution polymer or gel polymer. The diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer preferably has a RSV of from about 1 to about 10, more preferably from about 2 to about 8 and still more preferably from about 3 to about 6 dl/g and preferably comprises from about 10 to about 70, more preferably from about 18 to about 63 and still more preferably from about 25 to about 55 mole percent diallyl-N,N-disubstituted ammonium halide monomer. A preferred diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer is diallyldimethylammonium chloride/acrylamide copolymer.
xe2x80x9cAlkylxe2x80x9d means a monovalent group derived from a straight or branched chain saturated hydrocarbon by the removal of a single hydrogen atom. Representative alkyl groups include methyl, ethyl, n- and iso-propyl, cetyl, and the like.
xe2x80x9cAlkylenexe2x80x9d means a divalent group derived from a straight or branched chain saturated hydrocarbon by the removal of two hydrogen atoms. Representative alkylene groups include methylene, ethylene, propylene, and the like.
xe2x80x9cArylxe2x80x9d means an aromatic monocyclic or multicyclic ring system of about 6 to about 20 carbon atoms, preferably of about 6 to about 10 carbon atoms. The aryl is optionally substituted with one or more alkyl, alkoxy, halogen or haloalkyl groups. Representative aryl groups include phenyl or naphthyl, or substituted phenyl or substituted naphthyl. A preferred substituent is alkyl.
xe2x80x9cArylalkylxe2x80x9d means an aryl-alkylene- group wherein aryl and alkylene are defined herein. Representative arylalkyl groups include benzyl, phenylethyl, phenylpropyl, 1-naphthylmethyl, and the like. A preferred arylalkyl is benzyl.
xe2x80x9cAlkoxyxe2x80x9d and xe2x80x9calkoxylxe2x80x9d mean an alkyl-Oxe2x80x94 group wherein alkyl is defined herein. Representative alkoxy groups include methoxyl, ethoxyl, propoxyl, butoxyl, and the like.
xe2x80x9cHalogenxe2x80x9d means fluorine, chlorine, bromine or iodine.
xe2x80x9cHaloalkylxe2x80x9d means an alkyl group, as defined herein, having one, two, or three halogen atoms attached thereto. Representative haloalkyl groups include chloromethyl, bromoethyl, trifluoromethyl, and the like.
xe2x80x9cHydroxypropylenexe2x80x9d means a propylene group substituted with hydroxy.
xe2x80x9c(Meth)acrylamidexe2x80x9d means acrylamide or methacrylamide.
xe2x80x9cStructural modifierxe2x80x9d means an agent that is added to the aqueous polymer solution to control the polymer structure and solubility characteristics. The structural modifier is selected from the group consisting of cross-linking agents and chain transfer agents.
xe2x80x9cChain transfer agentxe2x80x9d means any molecule, used in free-radical polymerization, which will react with a polymer radical forming a dead polymer and a new radical. In particular, adding a chain transfer agent to a polymerizing mixture results in a chain-breaking and a concomitant decrease in the size of the polymerizing chain. Thus, adding a chain transfer agent limits the molecular weight of the polymer being prepared. Representative chain transfer agents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butyl alcohol, and glycerol, and the like, sulfur compounds such as alkylthiols, thioureas, sulfites, and disulfides, carboxylic acids such as formic and malic acid, and their salts and phosphites such as sodium hypophosphite, and combinations thereof. See Berger et al., xe2x80x9cTransfer Constants to Monomer, Polymer, Catalyst, Solvent, and Additive in Free Radical Polymerization,xe2x80x9d Section II, pp. 81-151, in xe2x80x9cPolymer Handbookxe2x80x9d edited by J. Brandrup and E. H. Immergut, 3d edition, John Wiley and Sons, New York (1989) and George Odian, Principles of Polymerization, second edition, John Wiley and Sons, New York (1981). A preferred alcohol is 2-propanol. Preferred sulfur compounds include ethanethiol, thiourea, and sodium bisulfite. Preferred carboxylic acids include formic acid and its salts. More preferred chain-transfer agents are sodium hypophosphite and sodium formate.
xe2x80x9cCross-linking agentxe2x80x9d or xe2x80x9cbranching agentxe2x80x9d means a multifunctional monomer that when added to polymerizing monomer or monomers results in xe2x80x9ccross-linkedxe2x80x9d polymers in which a branch or branches from one polymer molecule become attached to other polymer molecules. Preferred cross-linkers are polyethylenically unsaturated monomers. Representative preferred cross-linking agents include N,N-methylenebisacrylamide, N,N-methylenebismethacrylamide, triallylamine, triallyl ammonium salts, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, triethylene glycol dimethylacrylate, polyethylene glycol dimethacrylate, N-vinylacrylamide, N-methylallylacrylamide, glycidyl acrylate, acrolein, glyoxal and vinyltrialkoxysilanes such as vinyltrimethoxysilane (VTMS), vinyltriethoxysilane, vinyltris(xcex2-methoxyethoxy)silane, vinyltriacetoxysilane, allyltrimethoxysilane, allyltriacetoxysilane, vinylmethyldimethoxysilane, vinyldimethoxyethoxysilane, vinylmethyldiacetoxysilane, vinyldimethylacetoxysilane, vinylisobutyldimethoxysilane, vinyltriisopropoxysilane, vinyltri-n-butoxysilane, vinyltrisecbutoxysilane, vinyltrihexyloxysilane, vinylmethoxydihexyloxysilane, vinyldimethoxyoctyloxysilane, vinylmethoxydioctyloxysilane, vinyltrioctyloxysilane, vinylmethoxydilauryloxysilane, vinyldimethoxylauryloxysilane, vinylmethoxydioleyoxysilane, and vinyldimethoxyoleyloxysilane. A more preferred vinylalkoxysilane monomer is vinyltrimethoxysilane.
xe2x80x9cEmulsion polymerxe2x80x9d and xe2x80x9clatex polymerxe2x80x9d mean a water-in-oil polymer emulsion comprising a cationic, anionic or nonionic polymer according to this invention in the aqueous phase, a hydrocarbon oil for the oil phase and a water-in-oil emulsifying agent. Inverse emulsion polymers are hydrocarbon continuous with the water-soluble polymers dispersed within the hydrocarbon matrix. The inverse emulsion polymers are then xe2x80x9cinvertedxe2x80x9d or activated for use by releasing the polymer from the particles using shear, dilution, and, generally, another surfactant. See U.S. Pat. No. 3,734,873, incorporated herein by reference. Representative preparations of high molecular weight inverse emulsion polymers are described in U.S. Pat. Nos. 2,982,749; 3,284,393; and 3,734,873. See also, Hunkeler, et al., xe2x80x9cMechanism, Kinetics and Modeling of the Inverse-Microsuspension Homopolymerization of Acrylamide,xe2x80x9d Polymer, vol. 30(1), pp 127-42 (1989); and Hunkeler et al., xe2x80x9cMechanism, Kinetics and Modeling of Inverse-Microsuspension Polymerization: 2. Copolymerization of Acrylamide with Quaternary Ammonium Cationic Monomers,xe2x80x9d Polymer, vol. 32(14), pp 2626-40 (1991).
The aqueous phase is prepared by mixing together in water one or more water-soluble monomers, and any polymerization additives such as inorganic salts, chelants, pH buffers, and the like.
The oil phase is prepared by mixing together an inert hydrocarbon liquid with one or more oil soluble surfactants. The surfactant mixture should have a low hydrophilic-lypophilic balance (HLB), to ensure the formation of an oil continuous emulsion. Appropriate surfactants for water-in-oil emulsion polymerizations, which are commercially available, are compiled in the North American Edition of McCutcheon""s Emulsifiers and Detergents. The oil phase may need to be heated to ensure the formation of a homogeneous oil solution.
The oil phase is then charged into a reactor equipped with a mixer, a thermocouple, a nitrogen purge tube, and a condenser. The aqueous phase is added to the reactor containing the oil phase with vigorous stirring to form an emulsion. The resulting emulsion is heated to the desired temperature, purged with nitrogen, and a free-radical initiator is added. The reaction mixture is stirred for several hours under a nitrogen atmosphere at the desired temperature. Upon completion of the reaction, the water-in-oil emulsion polymer is cooled to room temperature, where any desired post-polymerization additives, such as antioxidants, or a high HLB surfactant (as described in U.S. Pat. No. 3,734,873) may be added.
The resulting emulsion polymer is a free-flowing liquid. An aqueous solution of the water-in-oil emulsion polymer can be generated by adding a desired amount of the emulsion polymer to water with vigorous mixing in the presence of a high-HLB surfactant (as described in U.S. Pat. No. 3,734,873).
xe2x80x9cDispersion polymerxe2x80x9d means a dispersion of fine particles of polymer in an aqueous salt solution which is prepared by polymerizing monomers with stirring in an aqueous salt solution in which the resulting polymer is insoluble. See U.S. Pat. Nos. 5,708,071; 4,929,655; 5,006,590; 5,597,859; 5,597,858 and European Patent nos. 657,478 and 630,909.
In a typical procedure for preparing a dispersion polymer, an aqueous solution containing one or more inorganic or hydrophobic salts, one or more water-soluble monomers, any polymerization additives such as processing aids, chelants, pH buffers and a water-soluble stabilizer polymer is charged to a reactor equipped with a mixer, a thermocouple, a nitrogen purging tube, and a water condenser. The monomer solution is mixed vigorously, heated to the desired temperature, and then a water-soluble initiator is added. The solution is purged with nitrogen while maintaining temperature and mixing for several hours. After this time, the mixture is cooled to room temperature, and any post-polymerization additives are charged to the reactor. Water continuous dispersions of water-soluble polymers are free flowing liquids with product viscosities generally 100-10,000 cP, measured at low shear.
In a typical procedure for preparing gel polymers, an aqueous solution containing one or more water-soluble monomers and any additional polymerization additives such as chelants, pH buffers, and the like, is prepared. This mixture is charged to a reactor equipped with a mixer, a thermocouple, a nitrogen purging tube and a water condenser. The solution is mixed vigorously, heated to the desired temperature, and then one or more water-soluble free radical polymerization initiators are added. The solution is purged with nitrogen while maintaining temperature and mixing for several hours. Typically, the viscosity of the solution increases during this period. After the polymerization is complete, the reactor contents are cooled to room temperature and then transferred to storage. Gel polymer viscosities vary widely, and are dependent upon the concentration and molecular weight of the active polymer component.
The polymerization reactions described herein are initiated by any means which results in generation of a suitable free-radical. Thermally derived radicals, in which the radical species results from thermal, homolytic dissociation of an azo, peroxide, hydroperoxide and perester compound are preferred. Especially preferred initiators are azo compounds including 2,2xe2x80x2-azobis(2-amidinopropane)dihydrochloride, 2,2xe2x80x2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2xe2x80x2-azobis(isobutyronitrile) (AIBN), 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile) (AIVN), and the like.
The polymerization conditions utilized herein are selected such that the resulting water-soluble structurally-modified polymer has a molecular weight of 2 million to 30 million and an intrinsic viscosity above 1, more preferably above 6 and still more preferably 15 to 30 dl/g. The reduced specific viscosity of the water-soluble structurally-modified polymer is generally above 3, preferably above 12 and frequently above 24 dl/g.
The structural modifiers are added to the reaction mixture after the start of polymerization of the monomers and prior to completion of polymerization of the monomers. They may be added all at once as a single treatment, or in portions. The level of modifier added to the aqueous polymer solution depends on the efficiency of the structural modifier, the polymer concentration, and the degree of polymerization at which it is added.
The degree of polymerization of monomers is determined by the change in the reaction density for water-in-oil emulsion polymerization, calorimeterically by measuring the heat of reaction, by quantitative infrared spectroscopy, or chromatographically, by measuring the level of unreacted monomer.
When a chain-transfer agent is the structural modifying agent, the chain-transfer agent may be added all at once as a single treatment, in portions, or in a manner such that the rate of addition parallels polymer conversion. In one embodiment, addition may be as a single treatment added after about 30%, preferably after about 50% polymerization of the monomers. The level of chain-transfer agent added is generally between from about 1 to about 30,000 ppm, preferably from about 25 to about 10,000 ppm and more preferably from about 50 to about 2,000 ppm based on monomer. When the chain-transfer agent is sodium hypophosphite, the level added is generally from about 2 to about 2000 ppm, preferably from about 100 to about 1000 ppm.
When the structural modifier is a cross-linking agent, the cross-linking agent is added after about 30%, preferably after about 50% polymerization of the monomers. The level of cross-linking agent is generally from about 0.1 to about 500 ppm, preferably from about 1 to about 50 ppm based on monomer. When the cross-linking agent is methylenebisacrylamide, the level is generally from about 0.5 to about 50 ppm, preferably from about 1 to about 10 ppm based on monomer.
When the cross-linker is a vinyltrialkoxysilane, the level of cross-linker is generally from about 0.1 to about 30,000 ppm, preferably from about 0.5 to about 15,000 ppm, more preferably from about 1 to about 3,000 ppm based on monomer. The vinyltrialkoxysilane may be added all at once as a single treatment, or in portions after the polymerization of the monomers has started, preferably after about 30 percent of the monomers have polymerized.
When the structural modifier is a combination of a cross-linker and a chain transfer agent, the amounts of each may vary widely based on the chain-transfer constant xe2x80x9cefficiencyxe2x80x9d of the chain-transfer agent, the multiplicity and xe2x80x9cefficiencyxe2x80x9d of the cross-linking agent, and the point during the polymerization where it is added. For example from about 1,000 to about 5,000 ppm (based on monomer) of a moderate chain transfer agent such as isopropyl alcohol may be suitable while much lower amounts, typically from about 100 to about 500 ppm, of more effective chain transfer agents such as mercaptoethanol are useful. Representative combinations of cross-linkers and chain transfer agents contain from about 1 to about 30,000 ppm, preferably from about 25 to about 10,000 and more preferably from about 300 to about 1500 ppm (based on monomer) of chain transfer agent and from about 1 to about 500, preferably from about 2 to about 100 and more preferably from about 5 to about 50 ppm (based on monomer) of cross-linker. A preferred combination of cross-linker and chain transfer agent is methylenebisacrylamide and formic acid and its salts, preferably sodium formate.
Preferred Embodiments
In a preferred aspect of this invention, the structural modifier is selected from the group consisting of cross-linking agents, chain transfer agents and mixtures thereof.
In another preferred aspect, the cationic monomer is dimethylaminoethyl acrylate methyl chloride quaternary salt and the acrylamide monomer is acrylamide.
In another preferred aspect, the structural modifier is selected from the group consisting of sodium formate, sodium hypophosphite, vinyltrimethoxysilane, methylenebisacrylamide, and combinations thereof.
In another preferred aspect, the structurally modified polymer is dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer.
In another preferred aspect, the dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer is composed of from about 5 to about 30 mole percent dimethylaminoethyl acrylate methyl chloride quaternary salt and from about 95 to about 70 mole percent acrylamide.
In another preferred aspect, the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer is diallyldimethylammonium chloride/acrylamide.
In another preferred aspect, the diallyldimethylammonium chloride/acrylamide copolymer is composed of from about 25 to about 55 mole percent diallyldimethylammonium chloride and from about 75 to about 45 mole percent acrylamide.
In another preferred aspect, the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer has a RSV of from about 1 to about 10 dl/g and the cationic structurally-modified water soluble polymer has a RSV of from about 12 to about 40 dl/g.
The effective amount of the structurally-modified water-soluble polymer and the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer depends on the characteristics of the particular papermaking furnish and can be readily determined by one of ordinary skill in the papermaking art. Typical dosages of the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer are from about 0.01 to about 10, preferably from about 0.05 to about 5 and more preferably from about 0.1 to about 1 kg polymer actives/ton solids in the furnish.
Typical dosages of the structurally-modified water-soluble polymer are from about 0.005 to about 10, preferably from about 0.01 to about 5 and more preferably from about 0.05 to about 1 kg polymer actives/ton solids in the furnish.
The order and method of addition of the cationic structurally modified polymer and diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer are not critical and can be readily determined by one of ordinary skill in the papermaking art. However, the following are preferred.
The cationic structurally modified polymer and diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer are dosed separately to the thin stock with the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer added first followed by addition of the polymer.
In another preferred method of addition, the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer is added to tray water, e.g. the suction side of the fan pump prior to thick stock addition, and the polymer to the thin stock line.
In another preferred method of addition, the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer is added to thick stock, e.g. stuff box, machine chest or blend chest, followed by addition of the structurally modified polymer in the thin stock line.
In another preferred method of addition, the diallyl-N,N-disubstituted ammonium halide/acrylamide copolymer and the structurally modified polymer are fed simultaneously to the thin stock like a single polymer program.
The retention and drainage properties of the furnish may also be improved by addition of a microparticle. For Example, U.S. Pat. Nos. 4,753,710, 4,913,775, 5,393,381 and 6,007,679 incorporated herein by reference, describe the use of cationic polymers and microparticles in a papermaking process.
xe2x80x9cMicroparticlesxe2x80x9d means highly charged materials that improve flocculation when used together with natural and synthetic macromolecules. Microparticles are used in combination with other wet end additives to improve retention and drainage on the paper machine. Microparticles encompass a broad set of chemistries including polysilicate microgel, structured colloidal silicas, colloidal alumina, polymers including copolymers of acrylic acid and acrylamide and naphthalene sulfonate/formaldehyde condensate polymers, bentonite and mineral clays such as montmorillonite, saponite and smectite types and colloidal silica in its many forms including modified colloidal silicic acids such as those described in PCT/US98/19339.
Representative copolymers of acrylic acid and acrylamide useful as microparticles include Nalco(copyright) 8677 PLUS, available from ONDEO Nalco Company, Naperville, Ill, USA. Other copolymers of acrylic acid and acrylamide are described in U.S. Pat. No. 5,098,520, incorporated herein by reference.
xe2x80x9cBentonitesxe2x80x9d include any of the materials commercially referred to as bentonites or as bentonite-type clays, i.e., anionic swelling clays such as sepialite, attapulgite and montmorillonite. In addition, the bentonites described in U.S. Pat. No. 4,305,781 are suitable. A preferred bentonite is a hydrated suspension of powdered bentonite in water. Powdered bentonite is available as Nalbrite(trademark), from ONDEO Nalco Company.
Representative dispersed silicas have an average particle size of from about 1 to about 100 nanometers (nm), preferably from about 2 to about 25 nm, and more preferably from about 2 to about 15 nm. This dispersed silica may be in the form of colloidal silicic acid, silica sols, fumed silica, agglomerated silicic acid, silica gels, precipitated silicas, and all materials described in Patent Cooperation Treaty Patent Application No. PCT/US98/19339, so long as the particle size or ultimate particle size is within the above ranges. Dispersed colloidal silica in water with a typical particle size of 4 nm is available as Nalco(copyright) 8671, from ONDEO Nalco Company. Another type of inorganic colloid used as a microparticle is a borosilicate in water; available as Nalco(copyright) 8692, from ONDEO Nalco Company. Other types of colloidal silica and modified colloidal silicas are commercially available from E.I. du Pont de Nemours and Co., Wilmington, Del. under the tradename Ludox(copyright), from Akzo Nobel, Surte, Sweden (BMA or NP Series), from Vinings Industries Inc., Atlanta, Ga. and from Nissan Chemical Industries, Ltd., Tokyo, Japan.
Representative naphthalene sulfonate/formaldehyde condensate polymers include Nalco(copyright) 8678 from ONDEO Nalco Company.
The amount of microparticle added to the papermaking furnish is from about 0.025 to about 5, preferably from about 0.05 to about 4 and more preferably about 0.1 to about 3 kilograms microparticle/tonne.
xe2x80x9cKilograms microparticle/tonnexe2x80x9d means kilograms of actual microparticle per 1000 kilograms of solids present in the furnish. The abbreviation for kilograms of actual microparticle per 1000 kilograms of solids present in the furnish is xe2x80x9ckg microparticle/tonnexe2x80x9d.
The microparticle is added to the papermaking furnish either before or after the structurally-modified polymer is added to the furnish. The choice of whether to add the microparticle before or after the polymer can be made by a person of ordinary skill in the art based on the requirements and specifications of the papermaking furnish.
The foregoing may be better understood by reference to the following examples that are presented for purposes of illustration and are not intended to limit the scope of the invention.